The present invention relates to an improved compact frame assembly for a press.
More particularly, the invention relates to an improved compact frame assembly for a press having two parallel opposed rolls for subjecting a moving web to pressure in a nip formed between the rolls, both of which have two ends. At least one of the rolls has a stationary support beam, a rotatable roll shell disposed about the beam and defining a space therebetween, and a roll shell support carried by the beam in the space for providing vertically-movable and rotatable support of the roll shell relative to the support beam. The compact frame assembly includes four bearing housing members adapted to be mounted one on each roll end for supporting the roll end at least pivotally. Each of the two bearing housing members for one of the rolls is adapted to be disposed at an adjacent one of the two bearing housing members for the other roll and form with said adjacent bearing housing member a pair of bearing housing members. The compact frame assembly further includes a device for interconnecting the two bearing housing members of each pair. The interconnecting device includes for each pair of bearing housing members at least two interconnecting members, and each member has a web portion and two rim portions projecting from the web portion. The bearing housing members have surfaces defining recesses for engagement with said rim portions so as to prevent the two bearing housing members of each pair from appreciably moving away from each other on loading of the press.
Although prestressed press framework of the type disclosed in U.S. Pat. No. 5,207,872 (Jansson) for a papermaking or boardmaking machine has proved to be excellent in most respects, in certain cases--such as when rebuilding the press sections of certain papermaking or boardmaking machines by substituting a shoe type press and associated framing for an existing high impact roll press and associated framing, for example--it will require a larger space than the one available. To overcome this disadvantage, a few compact frame designs have been developed, cf. U.S. Pat. Nos. 5,291,826 (Schiel) (=International Patent Publication No. WO 92/17641 (J. M. Voith)) and 5,305,689 (Schiel), International Patent Publication No. WO 93/12290 (J. M. Voith), and European Patent Publication No. EP-A- 0 553 462 (Sulzer-Escher Wyss), for example. These compact frame designs permit an easy substitution of a new felt for a worn one, the two first ones also permit an easy substitution of a new flexible roll shell for a worn one, and they form a platform on which the present invention is based.
In the compact frame designs disclosed in the WO 92/17641 and WO 93/12290, at their ends the two rolls are supported in bearing housing members. The bearing housing members of one roll are connected to those of the other roll by means of substantially I-shaped tie rods having hammer head ends. The tie rods are designed to be of relatively low flexural rigidity, and they are inserted from positions lateral of the rolls into recesses provided in the bearing housing members at locations closer to the load plane of the press. When the press is unloaded, each bearing housing member of one roll may be spaced a variable distance from the adjacent bearing housing member of the other roll or, alternatively, may support the adjacent bearing housing member indirectly over an intermediary member, which is removable in order to simplify an exchange of a press fabric extending through the press nip formed between the rolls. However, in an unloaded press the tie rods are not prestressed at all or just very little, so that also in the latter case a loading of the press will stretch the tie rods elastically and cause the forming of a gap between the intermediary member and the bearing housing member that in an unloaded press is supported thereby. The tie rods may be 0.7 to 1.5 meters in length, and the elastic stretching of them results in a larger required stroke of the press shoe in order to bridge the formed gap and achieve the desired pressing effect in the extended nip. The disclosed design permits axial displacement of a bearing housing member in relation to the intermediary member and the other bearing housing member of a pair to compensate for changes in length caused by thermal expansion or contraction of the stationary support beam or the rotatable roll shell, for example. On the other hand, a long stroke of the press shoe is disadvantageous. For example, when the press shoe is included in a shoe type press roll having a flexible roll shell for forming an extended press nip, a long stroke will expose the flexible roll shell to larger stresses and, consequently, contribute to a reduction of the life of the flexible roll shell.
When the two bearing housing members of a pair are not rigidly pressed against each other, there is some risk of one of them becoming dislocated to a position at the side of the load plane of the press. A dislocation will cause the nip pressure profile to vary in the cross machine direction. To solve this problem, the WO 93/12290 proposes the use of guide surfaces that extend parallel to the load plane and maintain the two bearing housing members of a pair in proper alignment also when they move away from each other.
Also in the compact frame design disclosed in the EP-A- 0 553 462 the bearing housing members of one roll are connected to those of the other roll by means of substantially I-shaped tie rods that are parallel to the load plane of the press. However, in this case the tie rod ends are enlarged to a semicircular shape, the straight boundary line of which forms the end face of the tie rod. As before, the bearing housing members are provided with recesses for engagement with the tie rods, but the tie rods are inserted into the recesses from positions axially outside of the bearing housing members. A removable intermediary member of a rectangular cross section may be partly embedded in each of the two bearing housing members of a pair in order to absorb any occurring shear forces. This design is unstable in the machine direction and requires that the bearing housing members of at least one of the rolls are supported in the machine direction by roll standards or the like. Although it is stated in the EP-A- 0 553 462 that by removing the intermediary member and the tie rods an exchange of the flexible roll shell can be carried out without any problems, the drawing clearly shows that it is impossible to exchange the flexible roll shell without first removing one of the bearing housing members from the stationary support beam, because they are too large to pass through the interior of the flexible roll shell.